netdev - Re: [PATCH 4/4] net: improve the user pointer check in init_user

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Message-ID: <20200728084746.06f52878@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 28 Jul 2020 08:47:46 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jan Engelhardt <jengelh@...i.de>,
        Ido Schimmel <idosch@...sch.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        David Laight <David.Laight@...LAB.COM>, netdev@...r.kernel.org
Subject: Re: [PATCH 4/4] net: improve the user pointer check in
 init_user_sockptr

On Tue, 28 Jul 2020 08:36:43 +0200 Christoph Hellwig wrote:
> Make sure not just the pointer itself but the whole range lies in
> the user address space.  For that pass the length and then use
> the access_ok helper to do the check.
> 
> Fixes: 6d04fe15f78a ("net: optimize the sockptr_t for unified kernel/user address spaces")
> Reported-by: David Laight <David.Laight@...LAB.COM>
> Signed-off-by: Christoph Hellwig <hch@....de>

> diff --git a/net/ipv4/bpfilter/sockopt.c b/net/ipv4/bpfilter/sockopt.c
> index 94f18d2352d007..8b132c52045973 100644
> --- a/net/ipv4/bpfilter/sockopt.c
> +++ b/net/ipv4/bpfilter/sockopt.c
> @@ -65,7 +65,7 @@ int bpfilter_ip_get_sockopt(struct sock *sk, int optname,
>  
>  	if (get_user(len, optlen))
>  		return -EFAULT;
> -	err = init_user_sockptr(&optval, user_optval);
> +	err = init_user_sockptr(&optval, user_optval, *optlen);
>  	if (err)
>  		return err;
>  	return bpfilter_mbox_request(sk, optname, optval, len, false);

Appears to cause these two new warnings, sadly:

net/ipv4/bpfilter/sockopt.c:68:56: warning: dereference of noderef expression
net/ipv4/bpfilter/sockopt.c:68:56: warning: dereference of noderef expression